1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus and, more particularly, to a photoelectric conversion apparatus formed by using a large-area process, which is suitably used as a two-dimensional photoelectric conversion apparatus for performing a one-to-one read operation in, e.g., a facsimile apparatus, a digital copying machine, or an X-ray image pickup or imaging apparatus.
2. Related Background Art
Conventionally, as a document reader in a facsimile apparatus, a copying machine, an X-ray image pickup apparatus, or the like, a read system using a reducing optical system and a CCD type sensor has been used. With the recent development in photoelectric conversion semiconductor materials typified by hydrogenated amorphous silicon (to be referred to as a-Si hereinafter), there has been a remarkable development in a so-called contact type sensor, which is obtained by forming photoelectric conversion elements and a signal processing unit on a substrate having a large area, and designed to read an image of an information source through a one-to-one optical system. Since a-Si can be used not only as a photoelectric conversion material but also as a thin-film field effect transistor (to be referred to as a TFT hereinafter), a photoelectric conversion semiconductor layer and a TFT semiconductor layer can be formed at the same time.
Furthermore, switching elements such as a thin-film field effect transistor and a capacitive element exhibit good matching and have the same film structure. For this reason, these elements can be formed as a common film at the same time. In addition, a photoelectric conversion apparatus having a higher S/N ratio can be manufactured at a lower cost. Furthermore, since each capacitor has an insulating layer commonly used as an intermediate layer and can be formed to have good characteristics, a high-performance photoelectric conversion apparatus capable of outputting the integral value of pieces of optical information obtained by a plurality of photoelectric conversion elements with a simple structure can be provided. With the use of a low-cost, large-area, high-performance photoelectric conversion apparatus, a facsimile apparatus or X-ray apparatus with added values can be provided.
In manufacturing a photoelectric conversion apparatus having a large screen, it is difficult to completely remove minute dust in the manufacturing process, especially dust peeling off from the wall of a thin-film deposition apparatus in the process of depositing an amorphous silicon layer on a substrate, and dust left on a substrate when a metal layer is deposited thereon. For this reason, with an increase in the size of a substrate, it becomes more difficult to eliminate wiring (interconnect) failures caused by dust and the like, such as a short circuit and an open circuit (disconnection) of wiring layers. In manufacturing a large-screen photoelectric conversion apparatus 121 by using one substrate, as shown in FIG. 1, with an increase in the size of a substrate, the yield per substrate decreases, and at the same time, the lost revenues per substrate increase.
As described above, at present, it is difficult to sufficiently decrease the cost of a large-area photoelectric conversion apparatus using one large-area substrate. Under the circumstances, a large-area photoelectric conversion apparatus is manufactured by using a plurality of substrates, e.g., silicon wafers or thin glass plates, having photoelectric conversion elements formed on their surfaces, and mounting the substrates on a base in the form of an array.
FIG. 2A is a schematic plan view showing such a photoelectric conversion apparatus obtained by two-dimensionally arranging a plurality of substrates. FIG. 2B is a schematic side view of the apparatus. Referring to FIGS. 2A and 2B, the apparatus includes substrates 1 and a base 2. An adhesive 51 is used to fix the substrates 1 to the base 2.
As the substrates 1, silicon wafers or thin glass plates are generally used. The thickness tolerance of silicon wafers is xc2x125xcexc. The thickness tolerance of thin glass plates is xc2x1200xcexc. In general, semiconductor elements are formed on the upper surfaces of the substrates 1. In mounting the semiconductor elements on the substrates 1, the lower surfaces of the substrates 1 are bonded to the base 2 in most cases.
When, however, the substrates 1 are fixed to the base 2 with the adhesive 51 with a constant thickness, the respective substrates 1 exhibit level gaps, resulting in considerable deterioration in the performance of the photoelectric conversion apparatus.
FIG. 2B is a schematic side view showing such a level gap B between the substrates. For the sake of easy understanding, the gap B is emphasized. As shown in FIG. 2B, thicknesses T1 and T2 of the substrates 1 exhibit a variation. If, therefore, a thickness t2 of the adhesive 51 is made constant, the upper surfaces (semiconductor element portions) of the respective substrates 1 are set at different levels, resulting in the level gap B between the substrates 1.
With the occurrence of the level gap B between the substrates, the distance between a phosphor formed on a given substrate, or an object (original), and a semiconductor element may increase beyond an allowable range. As a result, the object may become out of focus to cause a decrease in resolution or sensitivity.
When a phosphor is to be bonded to the semiconductor element surfaces of the substrates 1, since the semiconductor element surfaces of the substrates 1 in the array have different levels, it is impossible to tightly bond the phosphor to all the substrates 1. Even if the phosphor can be bonded to the substrates 1, such level differences may cause the phosphor to peel off.
Conventionally, in order to eliminate the level gap B and set the respective substrates at the same level, the substrates are polished to the same thickness in advance. Such a process, however, requires much time and many steps, resulting in an increase in cost.
It is an object of the present invention to solve the above problem by forming a large-area photoelectric conversion apparatus constituted by a plurality of substrates, each of which has photoelectric conversion elements mounted thereon, and which are arranged to be adjacent to each other, and to improve the performance of the photoelectric conversion apparatus.
It is another object of the present invention to realize a photoelectric conversion apparatus constituted by a plurality of substrates that are two-dimensionally arranged, in which the level gaps between the substrates are eliminated to solve problems such as a focus error, a decrease in resolution, a deterioration in sensitivity, and peeling of a phosphor bonded to the surface of each substrate, by a simple method.
It is still another object of the present invention to provide a photoelectric conversion apparatus in which substantially no changes in the spaces between adjacent substrates on a base occur, and no variation in the pitch of photoelectric conversion elements occurs.
It is still another object of the present invention to provide a photoelectric conversion apparatus having an arrangement which attains a high yield of products and a low cost and can solve the above problem, and a method of manufacturing the same.
It is still another object of the present invention to provide a photoelectric conversion apparatus constituted by a plurality of semiconductor element substrates arranged and fixed onto a base with an adhesive,
wherein levels of opposite surfaces of the plurality of substrates to the base are adjusted in accordance with a thickness of the adhesive, with which the substrates are bonded, such that the opposite surfaces are set within the same plane.
It is still another object of the present invention to provide a photoelectric conversion apparatus constituted by a plurality of substrates, each of which has photoelectric conversion elements, and which are bonded to a base to be adjacent to each other, wherein the substrates are bonded to the base with an adhesive having elasticity.
It is still another object of the present invention to provide a manufacturing method for a photoelectric conversion apparatus constituted by a plurality of semiconductor element substrates arranged and fixed onto a base with an adhesive, comprising the step of hardening the adhesive while a distance from an upper surface of the base to a semiconductor element surface of each of the substrates is kept to a design value.
It is still another object of the present invention to provide a mounting apparatus for a photoelectric conversion apparatus constituted by a plurality of semiconductor element substrates arranged and fixed onto a base with an adhesive, comprising means for holding the substrate until the adhesive hardens while a distance from an upper surface of the base to a semiconductor element surface of the substrate is kept to a design value.
According to the present invention, in a photoelectric conversion apparatus constituted by a plurality of substrates, each of which has semiconductor elements, and which are arrayed on one base having a plane, one array of substrates each having semiconductor elements are mounted such that the semiconductor element surfaces of the substrates are set within the same plane, and the respective substrates are fixed while variations in the thicknesses of the substrates are adjusted with the thickness of an adhesive.
According to the present invention, a plurality of substrates, each of which has photoelectric conversion elements mounted thereon, are bonded to a base with an adhesive resin to be adjacent to each other, and an elastic adhesive resin is used as the adhesive resin. A force produced by the difference in thermal expansion coefficient between the substrates and the base with a change in ambient environmental temperature or the like is absorbed by the elasticity of the adhesive resin, thereby suppressing variations in the spaces between the adjacent substrates and making the spaces between the adjacent substrates constant regardless of changes in ambient environmental temperature or the like.
According to the present invention, in a photoelectric conversion apparatus constituted by at least two substrates, each of which has photoelectric conversion elements two-dimensionally arranged and mounted thereon, and which are bonded within a plane, the difference in thermal expansion coefficient between the substrates, on which the photoelectric conversion elements are mounted, and a base is absorbed by a fixing adhesive resin having no elasticity and a semi-fixing adhesive resin having elasticity, which are used to bond the substrates, thereby making the spaces between the substrates substantially uniform regardless of changes in ambient environmental temperature.
In a photoelectric conversion apparatus constituted by two or more substrates bonded to a base, the problem caused by the difference in expansion coefficient between each substrate, on which photoelectric conversion elements are mounted, and the base is solved by a combination of coating weights and application positions of a fixing adhesive resin having no elasticity and a semi-fixing adhesive resin having elasticity, which are used to bond the substrates.
Adhesives used for bonding can be properly selected in accordance with the materials used for the bonding surfaces of the substrates and base which are bonded to each other. If the principal object is to adjust the level of each substrate, an adhesive exhibiting no or little contraction upon hardening is preferably selected.
An adhesive having elasticity is also preferably used for the following reason even if the adhesive is not completely uniform. When the photoelectric conversion apparatus is to read an object in tight contact, a read operation can be performed while the adhesive is made uniform by pressing it.
If, however, the apparatus is used in a pressed state, the use of the apparatus is undesirably limited. For this reason, an elastic adhesive without hardening contraction is preferably selected.
As a preferred adhesive which can be used for the present invention, an acrylic-based, epoxy-based, or silicone-based adhesive is available. As an adhesive resin having elasticity, especially rubber-like elasticity, a silicone-based adhesive resin, a butyl-rubber adhesive resin, a polysulfide-based adhesive resin, a styrene-rubber-based adhesive resin, a nitrile-rubber-based adhesive resin, or a chloroprene-based adhesive resin an be used.
As is apparent, as an adhesive resin, a one-part or two-part adhesive may be used. These adhesives may be used in combination or mixed, as needed.